1. Field of Invention
The present invention relates to a surface light source device generating a light flux illuminating an image display unit, such as LCD panel, of a display and to a display, such as LCD, which employs the surface light source device. The present invention also relates to a light guide plate which is employed in the surface light source device or display.
2. Related Art
It has been well known that a display for digital still cameras, digital video cameras, portable telephones, electronic pocket notebooks, car navigation devices, portable personal computers or liquid crystal television sets comprises an image display unit, such as LCD panel, illuminated by a surface light source device.
In general, a surface light source device comprises a primary light source such as fluorescent lamp or LED and a light guide plate having a side face (incidence face) through which the light guide plate is supplied with light of the primary light source. The light supplied by the primary light source is introduced into the light guide plate, propagating in the light guide plate. As known well, the emission face emits light on the way of this propagating. The emitted light is supplied to an image display unit such as LCD panel directly or via an additional member such as light diffusion plate or prism sheet.
In surface light source devices of such type, all surface of light guide plate except the incidence face and emission face usually faces any reflection member, thereby causing much of light leaking from faces other than the emission face to return into the light guide plate without being loss. The light returned gets a chance of emitting from the emission face.
Any technique is required for causing an emission face of a light guide plate in such a surface light source device of such type to provide a uniform emission. If no technique in particular applied, in general, a highly bright region appears impartially on the emission face in the vicinity of an end portion near to a primary light source. Further to this, brightness tends to decrease according to an increasing distance from the primary light source. If such uneven brightness is not reduced, the image display unit illuminated by the surface light source device provides an uneven image brightness, leading to undesirable visual effects.
For avoiding this, a prior art such as disclosed in Japanese Patent Laid-open (Tokkai-Hei) 1-241590 is employed. According to the prior art, a light diffusion pattern is formed on a back face (rear face) opposite with an emission face (front face) so that light diffusion ratio gets larger according to an increasing distance from a primary light source. This promotes emission from an area which is apt to show a reduced brightness well relatively, leading to a uniformalized emission intensity.
In recent years, however, such uniform brightness over an emission face does not always give the best condition. That is, some sorts of displays are often required to show a higher brightness in an area approximately at a center portion or other particular areas of an image display screen as compared with brightness around an end portion, under recent situation such that digital technology is broadly applied to displays and various image display manners are growingly employed.
For example, the above way is able to be applied really to a display such as digital still camera or digital video camera employing image-screen-center-portion focusing, the higher-brightness area can provide an emphasized image which is easier to see as compared with that provided in cases where a display unit is irradiated by an illumination light of an uniform brightness. Therefore, there arises demand for technique for giving a relatively high brightness to an approximately center portion or other particular portion(s) of an emission face of a light guide plate.
The the present invention has been proposed to give answer to such demand, being applied in the first place to a surface light source device comprising a light guide plate, having a major face to provide an emission face and another major face to provide a back face opposite with said the emission face, and a primary light source disposed in the vicinity of an end portion of said light guide plate, said primary light source supplying light to be introduced into said light guide plate and then to be emitted from said emission face.
According to a feature of the present invention, a first light diffusion pattern is formed on said back face, said first light diffusion pattern consisting of light diffusion elements distributed as to tend to get denser according to an increasing distance from said primary light source, and a particular partial region and surrounding region around the particular partial region is defined in said emission face, and a second light diffusion pattern is formed in said particular partial region so that said particular partial region provides a higher emission brightness as compared with that provided by a vicinity around said particular partial region.
This feature enables emission from the particular partial region to have a relatively high brightness. As a result, the foresaid demand is satisfied.
Typically, said particular partial region is located approximately at a center of said emission face. In this case, a high-brightness emission region is provided at an approximately center portion of the emission face in correspondence to the particular partial region.
The second light diffusion pattern may be also formed at least in a part of said surrounding region. The second light diffusion pattern may consist of light diffusion elements which are distributed more densely in said particular partial region as compared with in the surrounding region.
The second light diffusion pattern may consist of light diffusion elements each of which is smaller than each of light diffusion elements of which the first light diffusion pattern consists, the light guide plate may have a wedge-like cross section so that thickness gets smaller according to an increasing distance from said primary light source.
In the next place, the present invention is applied to a display comprising a surface light source device and an image display unit supplied with illumination light from a surface light source device. The display in accordance with the present invention adopts the above-featured surface light source device as a surface light source device for supplying illumination light to the image display unit.
In other words, the surface light source device includes a light guide plate, having a major face to provide an emission face and another major face to provide a back face opposite with said the emission face, and a primary light source disposed in the vicinity of an end portion of said light guide plate, said primary light source supplying light to be introduced into said light guide plate and then to be emitted from said emission face.
And a first light diffusion pattern is formed on said back face of the light guide plate, said first light diffusion pattern consisting of light diffusion elements distributed as to tend to get denser according to an increasing distance from said primary light source, and a particular partial region and surrounding region is defined in said emission face, and a second light diffusion pattern is formed in said particular partial region so that said particular partial region provides a higher emission brightness as compared with that provided by the region around said particular partial region.
This feature enables the image display unit to have a high-brightness displaying region in correspondence to said particular partial region.
Typically, said particular partial region is located approximately at a center of said emission face. In this case, a high-brightness image displaying region is provided in correspondence to the approximately center portion of the emission face.
A third light diffusion pattern may be formed at least in a part of said surrounding region. It is noted that no light diffusion pattern may be formed in said surrounding region.
The second light diffusion pattern may be also formed at least in a part of said surrounding region. The second light diffusion pattern may consist of light diffusion elements which are distributed more densely in said particular partial region as compared with in the surrounding region.
The second light diffusion pattern may consist of light diffusion elements each of which is smaller than each of light diffusion elements of which the first light diffusion pattern consists, the light guide plate may have a wedge-like cross section so that thickness gets smaller according to an increasing distance from said primary light source.
The present invention is further applied to a light guide plate having a major face to provide an emission face, another major face to provide a back face opposite with said the emission face and an incidence face through which light is introduced to be emitted from said emission face.
According to a feature of the present invention, a first light diffusion pattern is formed on said back face, said first light diffusion pattern consisting of light diffusion elements distributed as to tend to get denser according to an increasing distance from said primary light source, and a particular partial region and surrounding region, around the particular partial region, is defined in said emission face, and a second light diffusion pattern is formed in said particular partial region so that said particular partial region provides a higher emission brightness as compared with that provided by the region around said particular partial region.
This feature enables to the light guide plate to provide a high-brightness region in correspondence to said particular partial region when light is inputted on into the light guide plate.
Typically, said particular partial region is located approximately at a center of said emission face. In this case, a high-brightness emission region is provided in correspondence to the approximately center portion.
The second light diffusion pattern may be also formed at least in a part of said ordinary region. The second light diffusion pattern may consist of light diffusion elements which are distributed more densely in said particular partial region as compared with in the ordinary region.
The second light diffusion pattern may consist of light diffusion elements each of which is smaller than each of light diffusion elements of which the first light diffusion pattern consists, the light guide plate may have a wedge-like cross section so that thickness gets smaller according to an increasing distance from said primary light source.